Separation of hydrocarbons having different degrees of saturation



PatentedJmuZl, 1 947 ortica SEPARATION F HYDROCARBONS HAVING DIFFERENT DEGREES 0F SATURATION Howard S. Notting and Lee H.

Mich. assignors to The Dow Horsley, Midland, Chemical Company, Midland, Mich., a' corporation of Michi- Application July 31, 1942, serial No. 452,992

13 Claims. 1

This invention concerns an improved method of separating from hydrocarbon mixtures low boiling aliphatic hydrocarbons which normally tend to distill together but which are of different degrees of saturation. It pertains especially to a method for separating from one another such aliphatic hydrocarbons containing from 3 to 6 carbon atoms in the molecule and having the respective empirical formulas CnHzn and CnHzn-z, and it particularly concerns the separation of butylenes and butadiene-1.3 from mixtures thereof.

Deanesly, in United States Patent 1,866,800, shows that a liqueed mixture of a saturated paramnic hydrocarbon and a corresponding oleine, e. g. a mixture of bu'tane and butylene, may be separated into its components by fractionally distllling the mixture in the presence of liquid anhydrous ammonia to obtain a distillate consisting largely of the parainic hydrocarbon, e. g. butane, and ammonia, while continuously returning either a portion of the distillate or the anhydrous ammonia layer of the distillate as redux to the upper portion of the distilling column. A mixture consisting largely of ammonia and the olene, e. g. butylene, is obtained as the residue from the distillation. He teaches that the liquid anhydrous ammonia has a greater solvent action for butylenes than for butane and as a consequence that it lowers the vapor pressure of butylenes to greater extent than that of butano and thus permits separation of the hydrocarbons.

The present application is a continuation-iupart of our copending applications, Serial No. 330,205, led April 17, 1940, and issued March 13, 1945, as Patent No. 2,371,350, and Serial No. 287,218, filed July 29, 1939, which application Serial No. 287,218 is in turn a continuation-inpart of an earlier application, Serial No. 199,600,

Bled April 2, 1938. In said copending application, Serial No. 287,218. we have disclosed that aliphatic hydrocarbons containing less than 7 carbon atoms in the molecule (with the possible exception of certain of such acetylenic hydrocarbons) form minimum azeotropes with ammonia, i. e. azeotropes which are of lower boiling point than that of any individual component. closed that such hydrocarbons having different degrees of saturation but close to the same boiling point, e. g. butylene and butadiene, form azeotropes with ammonia which may be separated by fractional distillation. The distillation is usually carried out at super-atmospheric pressure, e. g. at pressures between 100 and 440 pounds per square inch gauge, although it may be carried out successfully at atmospheric pressure. .The pro- A4:5 It is also disportion o1' ammonia may be varied widely, provided suiilcient ammonia is present at all times to dlstlll in azeotropic admixture with the more nearly saturated hydrocarbon. In practice the proportion of ammonia is preferably restricted to approximately that required to distll together with the more saturated hydrocarbon, sincathe fractionation appears to occur most emciently when this is done and the residual less saturated hydrocarbon is obtained directly in a form nearly free of ammonia.

Said copending application, Serial No. 287,218 is directed particularly to the separation in concentrated or puried form of such unsaturated hydrocarbons having the respective empirical formulas CnHzn and CnHznaz from more complex hydrocarbon mixtures, e. g, cracked oil gas, by repeated fractional distillations of the hydrocarbon mixtures, alternately in the presence and in the absence of ammonia. The application con-'- tains no statement or restriction as to the concentration of the ammonia to be added to the hydrocarbon mixtures, although in certain of the examples liquid ammonia is used.

In the aforementioned copending application, Serial No. 330,205, we have disclosed that the separation of close-boiling hydrocarbons of different degrees of saturation by fractional distillation in the presence of ammonia may most advantageously be accomplished by employing the ammonia in approximately the proportion required to distill as an azeotrope together with the more nearly saturated vhydrocarbon and lby supplying less than half of the heat required for the distillation by means of a heater situated at the lower end of the distilling column and supplying the major portion of the heat at a point part way up the column. It is shown that by operating in this particular manner, the major portion of the heat may be supplied directly to the azeotrope of ammonia and the more nearly saturated hydrocarbon at a lower temperature (and hence, at lower cost) than when all of the heat is provided near the lower end of the column, and that the productive capacity of the column may be increased over that which it possesses when the heat for the distillation is all supplied at the lower end thereof.

The present invention concerns an improved method of carrying out azeotropic distillations of low boiling aliphatic hydrocarbons together with ammonia such as the azeotropic distillations described in the above-discussedcopending application, Serial No. 287,218. We have found that laqueous ammonia, i. e. ammonia diluted with 0.5

astma: j

per cent or more of water, may advantageously .be employed in carrying out such azeotropic distillation. The fractions of distillate obtained are for periodic interruption of the process and cleaning of the apparatus. The deposit that gradually accumulates when anhydrous ammonia is used in carrying out such distillation usually comprises polymeriz'ed dioleflnes and frequently also c ontains carbamates formed by reaction of the ammoniay with the small portion oi.carbon dioxide which almost invariably occurs in the commercialJy available hydrocarbon mixtures subjected to the treatment.O As just mentioned, the presphases` and 1n some instances only a trace of water is required to effect the separation. The water may be used in as large a proportion as desired. During such treatment of the ammoniacal distillate with water, heat is generated Land the. mixture is preferably maintained atsl temperature and pressure such as to avoid vaporiz'ation. The `added water forms a solution with the ammonia, thus forming the"'ammonia l'ayer of the mixture, and this layer is, of course, separated from the hydrocarbon layer and returned to the distillation.

We have further found that the water which accumulates at the bottom of the column during the azeotroplcdistillation may advantageously'be withdrawn continuously and be used to scrub any ence of water in the distilling mixture prevents appreciable accumulation` of deposits on the inner walls of the apparatus and it appears to prevent, or at least curtail. the formation of solids or tars in the distilling mixture.

The water may be recycled or fed into the process in such manner as to avoid the extensive cooling or refrigeration otherwise required in certain steps of the process. The azeotropic mixtures of ammonia and aliphatic hydrocarbons which are collected as distillates in the process may in all instances be caused to separate into` an ammonia layer and a hydrocarbon layer by cooling, but strong cooling or refrigeration is required in most instances to effect such separation. For instance, the critical solution temperature," i. e. the highest temperature at which any of the solutions of liquid anhydrous ammonia and a given hydrocarbon will separate into distinct' phases of ammonia and the hydrocarbon, is: 8 C. for the system of ammonia and propylene; below 78 C. for the system' of ammonia and y methyl-acetylene; 10 C. for. ammonia and butylene-1; 31 C. for ammonia and butadiene-1.3; below 78 C. for ammonia and vinyl-acetylene; and 22? C. for the system ammonia and amylene- 1. With regard to any of these systems, the hydrocarbon is appreciably soluble in ammonia at temperatures -below the critical solution temperature, and vice versa. Even a solution of anhydrous ammonia and a parafilnic hydrocarbon such as butane must be strongly cooled in order vto effect4 rapid. and substantially complete seperation of the ammonia and the hydrocarbon as distinct phases, e. g. butane is appreciablry soluble in anhydrous ammonia at 25-30 C.

We have found that by adding the water which is desired in the distillation to any such ammoniaand hydrocarbon fraction of thel distillate,sep aration of the ammonia and the hydrocarbon into distinct layers may be obtained without 'refrigeration. The proportion `of Water required to eii'ect the separation depends, of course, upon the kind and Aproportion of hydrocarbon in theffraction under treatment and upon the temperature at which the treatment is carried out. The addition of from 5 to 15 per cent by weight of Water is usually sufficient to causeV separation of the ammonia and the hydrocarbon into distinct deposits within the residualammnia from the distilled hydrocarbon product after separation of the latter from the ammonia layer of the distillate. The saving in ammonia, 'otherwise lost from the system, which is achieved by this scrubbing operation is considerable and greatly reduces the cost of the disbefore mentioned, the water thus continuously recycled in the process serves the three distinct functions of: (1) preventing the accumulation of distillation apparatus, particularly on the heating elements thereof, whereby it renders possible eiiicient heating of the distillingy lmixture "over long periods, of time; (2) causing separation of the solution of ammonia and hydrocarbon collected as distillate into a'hydrocarbon layer and an yammonia layer at temperatures far higher than would otherwise be required, whereby refrigeration of the distillate is avoided; and (3) scrubbing residual ammonia from the distilled hydrocarbon product;

We have also found that in carrying out such fractional distillation of close-boiling hydrocarbons gf dierent degree s\of saturation in the presence of ammonia and water, the proportion of ammonia may advantageously be restricted tof approximately that required to distill together with the more nearly saturated hydrocarbon or hydrocarbons and the major portion of the heat required for ythe distillation may advantageously be supplied by means of a calandria or other heater situated part way up the column, in which case only a minor part of the heat is-supplied at a higher temperature to the residual mixture of waterv and the less saturated hydrocarbon or hydrocarbons in the lower end of the distillin column. The advantages of operating in this particular manner are numerous, e. g. the water, as hereinbefore mentioned, serves to maintain the distilling apparatus, particularly the heaters, free of solid or tarry deposits; the major portion of the heat is supplied part way up the column directly to the ammonia-hydrocarbon azeotrope to be distilled, so that heating of the residual less saturated and least stable hydrocarbon is curtailed; the less saturated hydrocarbon may be obtained directly in a form nearly free of ammonia and the more nearly saturated hydrocarbon; and the productive capacity of the distilling Accordingly,

'heat results, ofv course, in an calandrias.

that whichit possesses when all of the heat for the distillation is su plied at the lower end of the column.

It may be explained that the increase in productive capacity of the' columnl thus attained is due to the fact that the ammonia-hydrocarbon systems dealt with have certain unusual characteristics; viz., the azeotropes` of ammonia and the hydrocarbons, although of'i lower boiling point than the hydrocarbons alone, have farhigher heats of vaporization than dgthe hydrocarbons.

the amount ot auch azeotrope vaporized per unit input ofs heat (e. g. by means of a heater situated part way up the column) is smaller than the amount of hydrocarbon vaporized by introducing the same amount ofheat directly to the the bottom of the column. The reduction in the amount of material vaporized per unit input of increase in the productive capacity of the column.-

'Ihe accompanying drawing is a diagrammatic 5 column is increased over I sketch showing one of the various arrangements of apparatus which may be employed in carrying out the process in continuous manner. In the drawing, the numeral I designates a distilling column which is provided near its mid-section with an inlet 2 for hydrocarbons and another inlet 3 for ammonia and at its lower end with a heater l and an outlet line I8.` At a point below the inlets 2 and 3 but part Way up the column, the latter may advantageously be provided, as shown, with the heater li, although such heater is not required. 4The heaters t and l may be as indicated, or other conventional heaters, e. g. boilers, or electric heaters. etc. At the top of column I is a vapor line 8 leading to a condenser l. Line 8 leading from the condenser branches into two valved lines ,9 and I Il. Line 9 is a reflux line which connects with column I near the top f the latter. Line I connects with a chamber Ilwhich may be a conventional settling chamber or a continuous separator as deand 5.

'.ifdesired hydrocarbon and water mixture at l butadiene to the l l answer form azeotropes with both the butylene and the butadiene or even an .excess over this amount, may be introduced if desired.

While' introducing the above-mentioned` starting materials, the distilling mixture is heated. e. g. by .passage of steam or other heating uuid through the principal chambers of calandrias l As hereinbefore mentioned, amajor' portion of the heat required for the distillation is preferably supplied by means of the heater l, but all of the heat may be supplied` by heater 4. The pressure on the distilling system determines the temperature at which the distillation is carried out and may be varied between wide limits. The distillation is usually carried out at pressures between 100 and440, preferably between 150 and 3 00, pounds per square inch gauge, but it may be carried out at lower ,pressures, e. g. at atmospheric pressure, if desired. Introduction of the mixture 'of butylene and distilling system may be continued for-as long a period as desired, e.. g. in practice the process has been operated continuously'without interruption over a period of several months. However,l ammonia is recycled continuously in the system; hence, the introduction of ammonia may be discontinued when suillcient ammonia to eiect the azeotropic distillation has been fed into the system.

The distilling column I, is operated so as to distill oi thebutylene togetherv with at least a portion of the in the residue. All except possibly a minorportion of thewater and also any excess of ammonia over that required to distill together with the butylene remain, of course, in the residue. In practice. the fractionation may be can-led out most eciently by restricting the proportion of sired. A valved line I2 leads from the lower end of chamber II and connects with the reflux line 9. Line I2 is ,provided with a valved branch line I3 which connects with column I near themidsection of thelatter. A line I4 lea`ds from the upper portion of chamber I I and connectswith i a scrubbing tower I5 near the lower end of .the

latter. .Tower I5 is provided toward its upper end with an inlet line 2I and with a valved outlet 26. A line 22 leads from the lower end of tower I5 to a pump 23. The latter is connected by line 2d with line Iii. The valved line IE, lead- `ing from the lower end of column I connects with a chamber Il, whichmay be a settlingchamber let 2 while lunder a pressure suiiicient to liquefy the same. Liquid ammonia, which may be anhydrous or may be an `aqueous ammonia solution of any desired concentration, is introduced through inlet 3. The ammonia is usually introduced in a liqueed form containing from 5 to 15 per cent by weight of4 Water and in amount suillcient to distill in azeotropic admixture with the butylene. A larger amount of ammonia, e. g. suiiicient to ammonia inI the distilling column to approximately that required to distill-together with the butylene. When operating in this preferred manner, the residue consists substantially of butadiene and water. Y

The vapors of butyleneand ammonia flow through line 6 to the condenser 1. A portion of the condensate is returned continuously through lines 8 and 9 to the top of column I for'purpose of reflux. The remainder of the condensate ilows from line 8 into line IIJ where it is treated with water, or with a dilute aqueous ammonia solution, which is introduced into line I0 from line 24. The proportion of Water thus added to the distillate usually corresponds to between 5 and 15 per cent of the weight of the latter, but the water may be added in smaller or in much larger proportion if desired.

The` resultant mixture flows to chamber II where it separates into an upper layer of butylene and a lower layer of aqueous ammonia.. The latter is returned either through lines I2 and 9 to the upper portion of column I` as reihix material or through line I2 and the branch line I3 as feed near the mid-section of column I In practice, the return fiowof the aqueous ammonia layer may be split so that a portion thereof is fed into the top of' column vI as reflux material and a portion is returned to the mid-section of the column.

The upper butylene layer of the distillate flows through line I4 into the lower section of scrubhing tower I5 where it is scrubbed with water to remove and recover any residual ammo-nia. therefrom. The purified butylene leaves the system through outlet `26. The scrubbing water flows through line 22, pump 23, and line 24, to line I0, where it serves to dilute the distillate and cause separation o1' the same into distinct phases.

ammonia and leave the butadiene.

f residue also `contains water.

- When the process is first placed in operation usinganhydrous ammonia /as a feed to the column, the still residue may consist substantially of butadiene alone or of a ammonia, but after operating'for some time the In any caselt is passed through line I 5 to chamber I1 whereit is treated, 'if necessary, with water (introduced through inlet 2li)l to remove any ammonia from the butadiene. yAs hereinbefore mentioned, the water is recycled continuously in the system so that after operation of thev process for a short time the proportion of water required for separation of the ammonia fromr the butadiene accuinulates together with the latter in the still residue, in which case water need not be introduced through inlet 25. The lower aqueous layer in chamber I1 (which layer contains any ammonia present) is passed through line' I9, pump 20, and line 2i to the upper portion of tower I5, where utilized, as hereinbefore mentioned, to scrub any ammonia from the butylene product. The upper layer of purified butadiene is withdrawn from chamber I'I through outlet I3.

Other hydrocarbon mixtures may be distilled together with ammonia as just described to separate from one another the hydrocarbons of different degrees of saturation which normally distill together. For instance, if the mixture of butylene and butadiene introduced through inlet 2 also contains ethyl-acetylene and/or vinyl acetylene, the aetylenic hydrocarbons accom- .pany the butadiene and are withdrawn together with the latter through outlet IB. The butadiene may thereafter be separated from the acetylenic hydrocarbons by careful fractional distillation in theabsence of ammonia. When .the mixture of butylene and'butadiene used as a starting mate- -rial also contains butane, the distillation may, if desired, be carried out carefully to obtain the azeotrope of `ammonia and butane as a rst, or more volatile, fraction4 and the residual mixture may be redistilled to obtain the azeotrope of ammonia and butylene as a second fraction. However, in practice it is usually most convenient to carry out a single distillation and to collect these two azeotropes together as a single fraction. The

distillation Vin the presence of aqueousammonia may, of course, be'applied with advantage in separating a mixture of a parafnic hydrocarbon and the corresponding olenne, e. g. a mixture of butane and butylene, into its components. The process as hereinbefore described may also be applied in separating from one another the hydrocarbons of close-to the same boiling pontbu-t having different degrees of saturation .which are contained in other low-boiling hydrocarbon mixtures. For instance, it may be applied in separating propane from propylene; in separating propylene4 from propadiene; in separating pentane from amylene; in separating amylene from pentadiene; or in separating a hexylene from a hexadiene; etc.

mixture of butadiene and butadiene product.

The continuous .method and the apparatus hereinbefore described may be modiiledor altered without departing from the invention. For instance, instead of introducing the water to the distllling system through inlet 25, it may be introduced at any of a number oi other suitable points in the system, e. g. alone or together with the ammonia through inlet 3. Also, the lheater 5 in column I is not essential and may be omitted.

' Furthermore, the invention may, if desired. be

carried out in batchwise manner using a, pot still provided with an emcient distilling column.

runs, both of which were ca .was carried out in the presence oi water. as here- ,oum modifications which may be made in the process will be apparent to those skilled in the art.

The followin exampiede'scribes comparative ed out in continuinbefore described. i

Examens Run 1 A liqueiied hydrocarbon mixture containing ap-I proximately 49.5 per cent by weight of butylene, 49.5 percent of butadiene-1.3, about 1 o f other ene and polymerization ture of phenol and tertiary-butyl-phenol) was fed at a rate of approximately 500 parts by weight per hour into a continuously operating still. Liquid anhydrous ammonia was at the same time introduced into the still, i. e. initially as feedstock and subsequently as recovered and recycled material, at a rate of approximately 425 parts per hour. Once the distilling system was in balance vinyl-acetylene) and 0.05 per` cent of a and sulcient ammonia had been added t0 distilll together with the butylene, the introduction of ammonia from a source outside of, the distilling system was discontinued except for periodic introduction of suilicient ammonia to make up for losses from the system. The ammonia thus added periodically as make up materialduring two months of continuous operation corresponded to 0.04 pound of ammonia pery pound of puried Heat was supplied. by the passage of steam through a calandria at the' lower end of the column and also through another calandria part way up the column. The distillation was carried out at a pressure of 200 pounds per square inch, gauge, and at a still-head temperature of about 30 C., whereby a solution of ammonia and butylene was obtained as the distillate. The latter was cooled by .refrigeration to 30 C., whereupon it separated into an ammonia layer containing only a small proportion of dissolved butylene and a butylene layer containing a small amount of ammonia. The layers were separated in a continuous separator and the ammonia was returned to the distillation.' The butylene layer was scrubbed with water to remove the small amount of dissolved ammonia f -tlerefro whereby butylene of approximately 98 per cent purity was obtained. The still residue, consisting principally of butadiene together with the acetylenic hydrocarbons and a trace of ammonia was washed with water and then'treated to remove the acetylenic hydrocarbons. The butadiene thusobtained was of approximately 98 per cent purity. The foregoing operations were carriedout continuously over a long period of time. Atfthe start of the distillation, steam was passed through the calandria at the lower end of the column under a pressure of 3 pounds per I square-inch gauge. However, as the distillation was continued, the inner surfaces of the tubes of this calandria gradually became coated with a sollddeposit, with` the result thatheat transfer became less elcient and the pressure on the steam passing through the Calandria had to be increased in order to supply the necessary heat to the distilling mixture. By the end of two months of continuous operation, .the.steam pressure in g scale. The runs.

per cent I hydrocarbons (principallyfethyl-acetylinhibitor. (consisting of a mix- 9 the lower calandria had been increased from anA initial value of 3 pounds per square inch to 10 pounds per square inch. The distillation was 10 ever. carried out continuously over a period of then interrupted and the calandria was cleaned.

A considerable amount of nlm-like deposit inthe form of a nearly solid tar was removed. Upon water also was fed into the still at a rate of 4$4 .except that resuming operation of the still, the distillation at parts by weight per hour. The steam pressure in the lower calandria required for continuance of the distillation thereafter gradually became less and ultimately was only 3 pounds per square inch, indicating that the calandria had been cleaned during operation in the presence of the water.

Run 2 A liqueed hydrocarbon mixture having the composition giveun in Run 1 was fed continuously into a distilling column at a rate of about 500 parts by weight per hour and liquid anhydrous ammonia was initially fed into the column-at a rate of approximately 425 parts per hour. The distilling column was the same as that employed in Run 1 and it was operated at the temperatures and pressuresgiven in said run. However, the still residue, consisting principally of butadiene was washed, as it owed from the column, with water which was introduced into the'system at a rate of about 64 parts by weight per hour. The butadiene, thus washed to remove any dissolved ammonia, was withdrawn from the system and was thereafter treated to remove the small por'- tion of acetylenic hydrocarbons which accom-.'

panied the same. Butadiene was obtained. The water which had been used to wash the still residue was circulated to a scrubbing tower where it was employed to scrub any dissolved ammonia from the butylene product.

of 98 per cent purity 'I'he water was next fed into admixture with the freshly accumulated distillate, whereupon it caused separation of the latter into an upper layer of butylene and a ammonia while at a temperature of about C. The layers were separated, the butylene layer being forwarded to the above-mentioned scrubbing tower where it was scrubbed, while in liqueed form, with water to remove any dissolved ammonia and was then withdrawn vfrom the system. Butylene of approximately 98 obtained. `The aqueous ammonia layer obtained by treatment of the distillate with the water was returned as reflux material to the distillation. The introduction of ammonia and water to the system was continued only until the system had lower layer of aqueous` per cent purity was been brought into balance with respect to these ingredients, i. e. until the rates of return of water and ammonia to the distilling column by recycling corresponded to those at which they had initially been introduced from outside sources. Thereafter the feed to the distillation system from an outside source consisted only of the mixture of hydrocarbons to be separated, except for occasional introduction of small amounts of ammonia and water to replace losses from the system. The ammonia thus added as make up material over a period of one month of continuous operation was measured and amounted to only 0.02 pound of ammonia per pound of purified butadiene. Operation as just described was, howseveral months. Throughout the entire period, steam was fed into the calandria at the lower end of the column under a pressure of 3 pounds per square inch, gauge. Heat transfer through the walls ofthe calandria occurred eillciently throughout the period of operation and the calandria remained clean and substantiallyfree of tar or other deposits.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made `as regards the method herein disclosed, provided the step or steps stated by any. of the following claims or the equivalent of such stated step or steps be employed. We therefore particularly point tinctly claim as our invention: y

1. In a method for separating from one another two aliphatic hydrocarbons containing more than 2 and less than 7 carbon atoms in the out and dismolecule and which tend to distill together but which have diierent steps of fractionally ture comprising said hydrocarbons in the presence of an appreciable amount of water and at least suflcient ammonia tov form a relatively low-,boiling azeotrope of ammonia and the more nearly saturated of said two aliphatic hydrocarbons, which azeotrope distills from the mixture, the presence of the water degrees of saturation, the

saturated of said two saturated hydrocarbon to leave the latter and the water in the residue, the water serving to prevent deposition of solids on the surfaces of the `distillation apparatus and thereby to facilitate eilicient operation of the process.

2. 'In a method wherein aliphatic hydrocarbons which tend to distill together and which are of different degrees of saturation and contain more than 2 and less than 7 carbon atoms in the molecule are separated from one another by fractional distillation at superatmospheric pressure in the presence of at least sumcient ammonia to form an azeotrope with the more nearly saturated of said hydrocarbons, the step of carrying the distillation out in the presence of an appreciable amount of water, whereby appreciable accumulation of solids on inner surfaces of the apparatus is prevented. Y f

3. In a continuous method wherein aliphatic hydrocarbons of different degrees of saturation and containing the same number of carbon atoms in the molecule, which number is more than 2 and less than 7, are separated from one another by fractional distillation at superatmospheric .pressure in the presence of sufiicient ammonia to distill off the more nearly saturated hydrocarbon in azeotropic mixture with ammonia and leave the less saturated hydrocarbon in the residue, the steps which consist in carrying the distillation out in the presence of an appreciable amount of Y water, ther latter serving to prevent the deposition of solids in appreciable amount on the inner mixture thus withdrawn from the column, and

while continuing said .operations treating the solution of ammonia and the moresaturated.

hydrocarbon obtained as the distillate with sumdistilling a hydrocarbon mixv cient water to causethe same to separate into hydrocarbon layer and1 an 'aqueous'ammonia layer, continuously returning the f latter tojthe distillationand scrubbing the hydrocarbon layer with the abueous layer separatecl-iromtheA still residue to extract any dissolved ammoniath'erefrom, and' thereafter water with'distillate, the water thus admixed with the distillate serving as that required to cause separation of the distillate into layers.-'

4. A method as described in :claim 2 wherein the 'empirical vformulas fori-the 'more nearly saturated andthe less saturated hydrocarbons are Cn'Hanfand CnHzq-z, respectively.'

5. A'mtnbd as 'described in 'claim 2 wherein the more nearly .saturated hydrocarbon is fan olene, the less saturated hydrocarbon is aconjugated dioleilne; andthedistillation is carried out at a" pressure between 1 00 and 440pounds per squarfilihn 6. A7 lnethod as h 1 i the more 'nearly saturated' hydrocarbon ls 'a butylene, `butadiene, A

a. pressure between 100 and 440 pounds per squareinch.-

LA method as described in claim'3 wherein the more nearly saturated hydrocarbon and the less ,saturated hydrocarbon havetheuempirical .formulas CnHm and QgHan-a, respectively.

8. A-inethod as described in claim aywherein the more nearly saturatedhydrocarbon lis an olene andthe less saturated hydrocarbon'is 'a lconjugated dioleilne.

9. A method as described in claim 3 whereiny the Amore nearly saturated hydrocarbon is a butylene and the less saturated hydrocarbon i's butadiene-1.3; i

10. A method as -described `in claim i"wherein the more.. ne arly saturated hydrocarbon is a nor- .mal .butylene,v the less saturated hydrocarbon is butadiene-1.3,. and the distillation is carried out at a pressure between 100 and 440 pounds per vsquare inch. i

11. In a method wherein aliphatic hydrocar- -bonswnicntend to distiu together anawmcn 'are of diierent degrees of saturation and contain more than 2 and less than 'I carbon atoms in .the molecule are separated from one another by frac- 'cnam admixing the scrbbing tional distillation in the presence of only sucient ammonia to `ar'fctrope with a portion of the hydrocarbons present, the steps which ,consist in carrying'the distillation out in the presence of waterap reclable amount not exceeding 15 perl centV ofthe :combined weight of the ammonia and water-while introducing a minor part of the heat required' for the distillation to the mixture "of hydrocarbon andwater in the lower portion ofv the stilland introducing the major part of the heat directly to the mixture rich in ammonia and hydrocarbonthereabove. l

12. A method as described in claim 11 wherein themore nearly saturated hydrocarbon has'thev empirical formula Cul-Im and the less saturated .hydrocarbon has the empirical formula CnHzn-a.

13. "Amethod as described, in 'claim 11 wherein v the hydrocarbons to be separated by theI distillal tion are an oleflne and a 'conjugated diolene '20 described in claim 2|' wherein having the same number of carbon atoms in the molecule' as the oleilne, a hydrocarbon'mixture comprising said hydrocarbons is fed in substantially continuous iiowin'to Ithe distilling system, the proportion of water in the distilling system corresponds to between about 5 and about 15 -per :cent of the combined weight of the ammonia and water, the still residue, comprising the diolene and lWater is withdrawn continuously from a lower portion ot the still and the aqueouss and organic layers thereof are separated, the distillate. comprising the voleilne and ammonia, is admixed with suiilcient water to cause formation of a hydrocarbon layer and an aqueous ammonia layer, the layers thus formed are separated and the hydrocarbon layer of the distillate is scrubbed with water to remove any dissolved ammonia therefrom, andwherein the water which is separated from the still residue is that employed to scrub dissolved ammonia from the hydrocarbon layer of the distillate, the resultant scrubbing water is the water which is admixed with the distillate to cause separation ofthe latter into the hydrocarbon layer and the aqueous ammonia 

